A method for operating a hybrid drive of a motor vehicle is generally known. In this context, the hybrid drive is designed, in particular, as a parallel hybrid drive, in which case a drivetrain of the motor vehicle includes a combustion engine and an electrical machine. They are permanently coupled to one another via a switchable separating clutch. If a separating clutch is provided, in addition to the operating modes of a hybrid driving, a boost operation and a recuperation operation, the drivetrain makes possible a purely electrical driving. The at least one electrical machine also has the task of supplying an electrical accumulator and an electrical system of the motor vehicle with the requisite electrical energy. In the case of high torque demand input by the driver, the combustion engine is assisted by the electrical machine. This so-called boost operation is only temporarily feasible (over the medium term) since energy is withdrawn from the electrical energy accumulator in the process. In addition, the electrical machine renders possible a recuperation operation, in which, during a deceleration of the vehicle, kinetic energy is converted into electrical energy by regenerative operation of the electrical machine. Moreover, the electrical machine is utilized to compensate for a delayed response of the combustion engine to a torque demand. A delayed response occurs, for example, in the context of what is generally referred to as turbo lag, or due to the limited airpath dynamics of the combustion engine. For the most part, combustion engines, in particular, Otto engines having manifold injection, have an electronic throttle valve for regulating the air mass flow rate. The gas pedal is mechanically decoupled from this electronic throttle valve.
The finite setting speed of the throttle valve actuator and the dynamic charge effects in the intake manifold (airpath) do not permit a highly dynamic adjustment of a predefined air mass flow rate and of the thereby generated combustion engine torque. In contrast to the airpath, an intervention into the ignition timing and a reduction in the combustion engine torque associated therewith can be effected virtually without delay. However, retarding the ignition timing to a later ignition point degrades the efficiency of the combustion engine and increases the fuel consumption and the exhaust emissions. The torque control of the electrical machine exhibits a dynamic response which is substantially greater than the turbo lag of a Diesel engine or the intake manifold dynamics of an Otto engine. For that reason, the electrical machine is used in the short- and medium-term operation to supplement the combustion engine. This supplementation must be coordinated in a way that ensures the operation of the vehicle electrical system over the long term.